1. Field of the Invention
This invention relates to a method and apparatus for providing liquid crystal display LCD control. More particularly this invention relates to a method and apparatus for displaying unscaled images on LCD panels without a frame buffer. The method and apparatus uses the same buffers available to the digital signal processor DSP for displaying the image.
2. Description of Related Art
Today, conventional LCD controllers utilize a scaling up mapping. FIG. 1 shows a mapping of a 640 by 480 pixel image 110 being displayed on a 1024 by 768 pixel LCD display 120. The figure illustrates a scaling up of the image to fit the LCD display, which has a larger pixel format (1024 by 768) than the image (640 by 480). The mappings 130 & 140 of the starting and finishing points of the image are shown in FIG. 1. The conventional circuit to perform the above scaling up operation requires a higher clock frequency to produce a display on the LCD panel. This higher frequency is required for the scaling up digital signal processor, DSP to keep the same frame rate as the smaller image. In addition, this convention implementation needs several line buffers for temporary data storage.
FIG. 2 shows the conventional implementation of the No-scaling LCD display. In this case, a frame buffer is required to capture the whole frame of image data so that the 640 by 768 image 210 can be displayed anywhere on the LCD panel's 1024 by 768 grid 220. The mappings 230 & 240 of the starting and finishing points of the image are shown in FIG. 2. A example to illustrate the conventional method's requirement for a frame buffer. If the source image is 640×480 and the LCD panel is 1024×768, the source frame time provided without a frame buffer would be defined by 480 Hsync pulses and the LCD image frame time is given by 768 Hsync pulses. The reason why the frame buffer must be used is because the frame time for the source image has to equal that of the entire larger LCD frame. However, the available frame time for the non-scaled display image is significantly less than that of the source image as illustrated above by the difference in the number of Hsync pulses.
U.S. Pat. No. 5,537,128 (Keene, et al.) “Shared Memory for Split-Panel, LCD Display Systems” describes a memory sharing method for a split panel LCD. The method enables efficient memory sharing and video processor usage between an LCD driver and a CRT driver in a common system.
U.S. Pat. No. 5,712,681 (Suh) “Apparatus for Inputting and Outputting an Optical Image with Means for Compressing or Expanding the Electrical Video Signals of the Optical Image” shows an apparatus capable of inputting and outputting an optical image. A means of compressing or expanding the electrical video data is provided. The circuit displays the captured image on an LCD panel.
U.S. Pat. No. 6,049,322 (Yoshikawa et al) “Memory Controller for Liquid Crystal Display Panel” provides a memory controller for an LCD panel. The apparatus allows the source driver for the LCD to operate at a lower frequency than the line buffer.